ECS Electrical Supply Systems and Distribution 2

Question 1

What is the standard frequency of the electrical supply in the United States?

Accepted Answer

60 Hz

Answer

The US electrical supply operates at a standard frequency of 60 Hz, meaning the AC current completes 60 full cycles per second.

Question 2

In a three-phase 208V/120V Wye system, what voltage would you measure between any two line conductors?

Accepted Answer

208V

Answer

In a Wye (star) configured system, the line-to-line voltage is the phase voltage multiplied by the square root of 3 (√3 × 120V ≈ 208V).

Question 3

What is the purpose of a sub-distribution board (SDB) in a large commercial electrical installation?

Accepted Answer

To distribute power locally within a zone, fed from the main distribution board

Answer

A sub-distribution board receives its supply from the main distribution board and distributes power to circuits within a specific area or floor of a building, reducing cable runs.

Question 4

Which type of electrical supply system uses a separate protective earth (PE) conductor and a neutral (N) conductor throughout the installation?

Accepted Answer

TN-S system

Answer

A TN-S system has separate neutral and protective earth conductors throughout the entire installation, providing the most reliable earth fault protection.

Question 5

What is the primary advantage of a ring main circuit over a radial circuit for socket outlet distribution?

Accepted Answer

It provides two paths for current, allowing smaller cable sizes for the same total load

Answer

A ring main circuit provides two current paths from the distribution board to any outlet, meaning each path carries approximately half the total current, allowing smaller cable sizes.

ECS - Electrotechnical Certification Scheme Practice Test

ECS - Electrotechnical Certification Scheme Practice Test

ECS Electrical Supply Systems and Distribution 2